Pipeline leak detection method



July 19, 1966 F. v. LONG 3,261,200

PIPELINE LEAK DETECTION METHOD Filed Feb. .11, 1964 2 Sheets-Sheet 1A770 IVEVJ July 19, 1966 F. v. LONG PIPELINE LEAK DETECTION METHOD 2Sheets-Sheet 2 Filed Feb. ll, 1964 INVENTOR.

United States Patent Office 3,261,200 Patented July 19, 1966 3,261,200PIPELINE LEAK DETEKITION METHOD Francis Vinton Long, Shreveport, La,assignor to Texas Eastern Transmission Corporation, Shreveport, La., acorporation of Delaware Filed Feb. 11, 1964, Ser. No. 34?,523 5 Claims.(Cl. 73-405) This application is a continuation in part of my copendingapplication Serial No. 114,110 for Pipeline Leak Detection Method, nowabandoned.

This invention relates to pipelines, and more particularly to thelocation of leaks in pipelines.

The development of effective hydrostatic testing of new pipelines hasproceeded far beyond the development of techniques to locate theoccasional leaks discovered when the pipe is tested. For many yearsthere has been a need for a simple technique which can be used under allfield conditions and in good and bad weather, as well as difficultterrain.

In the past, two methods have been used to locate leaks; one, to walkthe line and look for surface seepage; two, install manifolds and dividethe line into shorter and shorter test sections, and, when the last testsection becomes a reasonable length, strip the line and make a visualinspection.

The above procedures are slow, tedious and extremely expensive for thecost of installation of manifolds, final stripping of the last sectionof the line, and the loss of revenue time encountered, While many daysare consumed in this search.

It is an object of this invention to provide a practical acousticalsignal technique of detecting the position of a leak in a line underpressure.

Another object is to determine the approximate frequency of compressionwhich Will result from a leak in a given pipe and provide a system fordetecting sound at said frequency.

Another object is to provide a method of determining the approximateposition of a leak in a buried pipeline from compression sound wavesgenerated by the leak.

Another object is to provide a method of determining the approximateposition of a leak in a buried pipeline from compression sound wavesgenerated by the leak and measured at Widely spaced points in thepipeline to avoid the necessity of dividing lines into test sections andtesting small sections.

Another object of this invention is to determine the frequency at whichcompression waves would be generated by a leak and measure signals atthis frequency at widely spaced points in the pipeline and determiningthe distance of the leak from one of the measuring points by thefollowing relationship: The relationship of the sum of two signals readto the distance betwen the two signal reading pionts is .a function ofone reading to the unknown distance from the leak to the point at whichthe other signal was read.

Other objects, features and advantages of the invention will be apparentfrom the specification, the claims and the drawings.

In the drawings, wherein like reference numerals indicate like parts;

FIGURE 1 is a view in section of a pipeline being tested in accordancewith this invention; and,

FIGURE 2 is a sectional view illustrating a section of a pipeline beingtested in various types of terrain.

In the construction of cross-country pipelines of large diameter, it iscustomary to complete a substantial section of the line, say severalmiles, and then close off this section of the line, fill it with waterand pressurize the line to a hydrostatic pressure on the order of 1,000to 2,000 p.s.i. In FIGURE 1, the pipeline may be assumed to be severalmiles long and to have been buried underground in the usual manner.Water from a suitable reservoir 11 is pumped into the pipe 10 by pump 12and air exhausted from the line at the other end through valve 13 untilthe pipeline is substantially filled with water. Valve 13 is then closedand the line pressurized by pump 12 to a pressure on the order of 1,000to 2,000 p.s.i. If a leak is present, the location of the leak can bedetermined in accordance with this invention by sensing the intensity ofcompression waves generated by the leak.

It has been found that two sound Waves are generated by a leak in theWall of the pipe. One is the comparatively low frequency signal which iseasily heard outside the pipe and detected from the outside surface ofthe pipe. The signal is usually in the 500 to 3,000 c.p.s. range. Thislow frequency signal is audible and consists of a hissing sound. Theother type signal resulting from a high pressure leak is what may bereferred to as the organ tube signal. It is known that a tube which isopen at each end is resonant at a frequency such that the length of thetube is one-half wave length. If a pipe has a leak through its wall, theopening may be considered to be an organ tube. Thus, if we have a pipewhose wall thickness is .375 inch and the velocity of a compressionalWave in water is 57,000 inches per second, then the frequency of theorgan tube signal is f=V/ 2 Wall thickness=57,000/.75=76 kc It has beenfound that this high frequency signal will be transmitted through thecolumn of Water inside the pipeline for a considerable distance withrelatively low signal loss. It has further been found that the signalloss in traveling through the pipe is substantially a function of thedistance traveled by the signal.

In accordance with one aspect of this invention, hydrophones of anydesired type which are sensitive to the resonant frequency of the pipeare placed in the pipe at spaced points. Obviously these hydrophonesmight be placed in the pipe during construction or after construction inany desired manner, it only being necessary that they be positioned inthe pipe at some time and that their position in the pipe along itslength be known. Preferably, after it is discovered that a leak ispresent, hydrophones are placed in the pipe through the bosses 14 and15. Conventional cutting equipment is well known for both securing thebosses 14 and 15 to the pipe and for inserting tools such as hydrophones16 and 17 into the bosses and securing them therein. Leads 18 and 1%from the hydrophone 16 are connected to amplifier 21 and the signal fromamplifier 21 is fed to the meter 22 which indicates in decibels themagnitude of the signal at the resonant frequency of the pipe at thepoint Where the hydrophone 16 is positioned in the pipe.

In like manner, loads 23 and 24 from hydrophone 17 conduct the signalsensed at the point where hydrophone 17 is positioned in the pipe toamplifier 25. The amplified signal is then indicated by meter 25.

Preferably, the hydroplhone is one selected to be very sensitive tosignals of the frequency of the leak in the pipe and the amplifier 2 5would preferably be designed to also be sensitive to the frequency ofthe compression waves generated by the leak in the pipe and relativelyinsensitive to other frequencies to eliminate as many antifacts aspossible.

The distance between hydrophones 16 and 17 is measured and the sum ofthe readings of the meters 22 and 26 relative to this total distance isproportional to the relationship of one meter reading to the unknowndistance from the other meter to the leak. Thus, if the reading of meter22 is 70 db, the reading of meter 26 is 30 db, the distance betweenhydrophones 16 and 17 is two miles, and X equals the distance betweenthe leak indicated at 2'7 and 3 hydrophone 16, then 100/2 is equal to30/X and X=.6 mile. Thus, the distance between leak 27 and hydrophone 16is .6 mile. After this determination is made, the .6 of a mile fromhydrophone 16 is measured off and the backfill removed from over thepipe to permit visual location of the leak 27 and repair thereof.

After the leak has been repaired and the line retested, if desired thehydrophones may be removed and plugs inserted in bosses 1-4 and topermit their reuse at a later date. If desired, the hydrophones may beleft in place as expendable items.

Referring now to FIGURE 2, the pipe indicated generally at 28 is shownto have a portion 28a in relatively dry ground, a portion 28b in Wet,marshly land, and a portion 280 resting on the floor of a body of water.In this figure the invention is illustrated with transducers utilizedoutside of the pipe to detect leaks in the pipe. Again, the transducers29 and 31 are preferably designed to be sensitive to the frequency ofthe compression waves generated by the leak in the pipe and relativelyinsensitive to other frequencies to eliminate as many antirfacts aspossible. Again, the frequency of the wave is determined by theorgan-tube effect of the leak through the wall of the pipe, inaccordance with the formula given albove.

As fluid passes through a leak in the pipe, the compression waves aregenerated both internally and externally of the pipe, and, of course,will be present in the pipe wall itself. In this form of the invention,the transducers 29 are designed to pick up these external compressionwaves and the sound waves in the pipe itself. Where the pipe is abovethe water table, it is preferred that the transducer be in contact withthe pipe. IR is preferred that the transducer contact the pipe becauseair and soil are not good conductors and attenuate the ultrasonicfrequency waves. However, it is not necessary that the transducer be incon tact with the pipe, particularly where the transducer is close tothe leak.

As water is an excellent conductor of compression waves, it iscontemplated that the transducer may be placed adjacent the pipe and thesurrounding area flooded to provide a path for conducting sound.

The transducer 29 is carried on a probe 32. It is preferred that anotherinstrument, not shown, be used to punch a hole in the ground into whichthe probe 32 which carries the transducer is inserted.

The signal from the transducer 29 is fed to the tuned amplifier 25, ashereinabove explained, and the signal sensed is read on meter 26.

The: transducer 29 may be sensing the escape of either a gas or a liquidfrom the pipe 28.. While it is customary to test new lines with anincompressible fluid such as (water, they may be tested with acompressible fluid such as gas. The compression waves created by eitherescaping water or gas from pipe 28 may be sensed by the transducer 29.In like manner, it should be noted that the system shown in FIGURE 1 maybe utilized to sense waves created by escaping gas with transducerslocated internally of the pipe, because the compression waves willtravel down the wall of the pipe and also will travel internally of thepipe. It is preferred, however, that where the transducers are locatedinternally of a pipe that the test be carried out with an incompressiblefluid such as water.

Where the pipe is charged with methane gas, the velocity of acompressional wave in the gas will be 17,000 inches per second. Using apipe wall of .375 in., the frequency may be determined as follows:

F V/ 2 wall thickness: 17,000/.75=22,666 or 22.7 kc.

It will be appreciated that an escaping fluid, whether it becompressible or incompressible, will cause a readily detectable wavewhere the pipe is below the water table or beneath the surface of a bodyof water. This is true because water is incompressible and thecompression waves from the leak will pass through the water about theexterior of the pipe. As the attenuation of these waves is relativelysmall, the transducer may be located at a relatively greater distancefrom the pipe than in the case where no water is present. Thus, while itis preferred to have the transducer in contact with the pipe in drysoil, this is not necessary where the pipe is surrounded by water, asthe Water will make an excellent couple between the pipe and transducer.This is illustrated by the transducer of FIGURE 2 located in the marshyland and being spaced from the pipe.

When the pipe is resting on the bed of a body of water, the transducer31 may be towed behind a boat 33. Of course, the tuned amplifier 25 andmeter 26 will be located in the boat so that the operator may determinethe presence or absence and intensity of the frequencies received. Itwill be apparent that in the use of the transducers receiving acompression wave from the pipe wall or from the exterior of the pipe,that the operator will move the transducer along the pipe until thetransducer picks up acoustical waves at substantially the resonantfrequencies of the organ tube effect established by the thickness of thepi e wall. The transducer will then be moved along the pipe to determinethe direction in which the signal increases. Continued movement of thetransducer towards the leak will result in an increased signal until theleak is passed, when a decrease in signal will be noted. In this manner,the location of the leak is determined.

From the above, it will be seen that by designing the pickup apparatusto be sensitive to the resonant frequencies of the pipe as determined bythe organ-tube formula, that the equipment will pick up waves which arecaused by the leak in the pipe. As the equipment is designed to pick upthis frequency, it will tend to exclude other frequencies, thus greatlyincreasing the sensitivity of the system. While the waves created by theleak in the pipe are best transmitted through an incompressible medium,they will be transmitted to a lesser extent through a compressiblemedium, and thus the system may be used in testing a pipe containingeither a compressible or incompressible medium under pressure. As thewaves created by the leak are also transmitted down the pipe itself,these waves may be picked up by a transducer positioned exteriorly ofthe pipe. Where the pipe is surrounded by water, the waves travelingthrough this water are more readily sensed than is the case when thepipe is not covered by an incompressible medium. This feature is ofgreat advantage when the pipe is beneath the body of Water, as thetransducer may be towed along the pipe from a boat.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What I claim is: 1 The method of locating a leak in a pipelinecomprising:

closing the pipeline at both ends, filling the pipeline with Water underpressure, determining the resonant frequency of an open tube having alength equal to the pipe wall thickness,

sensing at widely spaced points in the pipeline any compression waves atapproximately said determined resonant frequency resulting from a leakin the wall of the pipeline with instruments sensitive to approximatelysaid resonant frequency,

measuring the amplitude of such compression waves sensed at spacedpoints,

and comparing the amplitude of compression waves measured to determinethe relative position of a leak from each sensing point.

2. The method of locating a leak in a pipeline comprising:

closing the pipeline at both ends,

filling the pipeline with an incompressible fluid under pressure,

determining the resonant frequency of an open tube having a length equalto the pipe Wall thickness, and

sensing at widely spaced points in the pipeline any compression waves atapproximately said determined resonant frequency resulting from a leakin the wall of the pipeline with instruments sensitive to approximatelysaid resonant frequency, measuring the amplitude of such compressionwaves sensed at spaced points, and comparing the amplitude ofcompression Waves measured to determine the relative position of a leakfrom each sensing point.

3. The method of locating a leak in a pipeline comprising,

filling the pipeline With a fluid under pressure to cause said fluid toescape through a leak in the pipeline,

determining the resonant frequency of an open tube having a length equalto the pipe wall thickness, and

sensing the compression Waves resulting from said escaping fluid atapproximately said determined resonant frequency with instrumentssensitive to approximately said resonant frequency and relativelyinsensitive to other frequencies.

4. The method of locating a leak in a pipeline comprising,

filling the pipeline with a fluid under pressure to cause said fluid toescape through a leak in the pipeline,

determining the resonant frequency of an open tube having a length equalto the pipe wall thickness, and

sensing the compression waves resulting from said escaping fluid atapproximately said determined resonant frequency with instrumentssensitive to approximately said resonant frequency and relativelyinsensitive to other frequencies and located exteriorly of the pipe.

5. The method of locating a leak in an underwater pipeline comprising,

filling the pipeline with a fluid under pressure to cause said fluid toescape through a leak in the pipeline,

determining the resonant frequency of an open tube having a length equalto the pipe Wall thickness, and

sensing the compression waves resulting from said escaping fluid atapproximately said determined resonant frequency with instrumentssensitive to approximately said resonant frequency and relativelyinsensitive to other frequencies and moving through the body of Wateradjacent the pipeline.

References Cited by the Examiner UNITED STATES PATENTS 882,141 3/1908Cope 73-40.5 X 3,000,205 9/1961 Suderow 73-405 X 3,028,450 4/1962Manning 7340.5 X 3,055,209 9/1962 Reid et a1. 73-40.5 X

LOUIS R. PRINCE, Primary Examiner. D. M. YASICH, Assistant Examiner.

1. THE METHOD OF LOCATING A LEAK IN A PIPELING COMPRISING: CLOSING THEPIPELINE AT BOTH ENDS, FILLING THE PIPELING WITH WATER UNDER PRESSURE.DETERMINING THE RESONANT FREQUENCY OF AN OPEN TUBE HAVING A LENGTH EQUALTO THE PIPE WALL THICKNESS, SENSING AT WIDELY SPACED POINTS IN THEPIPELINE ANY COMPRESSION WAVES AT APPROXIMATELY SAID DETERMINED RESONANTFREQUENCY RESULTING FROM A LEAK IN THE WALL OF THE PIPELINE WITHINSTRUMENTS SENSITIVE TO APPROXIMATELY SAID RESONANT FREQUENCY,